Ferroelectric random access memories (FeRAMs or FRAMs) are random access memories that use a ferroelectric layer to provide a nonvolatile memory capability. An FRAM, therefore, can hold data even after it is powered off.
FRAMs have many advantages over, for example, DRAMs, EEPROMs, and the like. For instance, FRAMs have fast write times, typically less than about 50 ns. Write operations to an FRAM occur at low voltage, and require very little current to change the data. In addition, FRAMs can endure 100 trillion read/write cycles or more without failing. Because of these advantages, the popularity of FRAMS is increasing for many applications.
However, FRAMs have a destructive read operation: a data write-back must be performed as part of a read operation in order to preserve the data held in the FRAM. Thus, in a read operation, the FRAM operating voltage must be maintained, typically at a minimum of 1.35V for about 110 ns, for a good read and write-back cycle. If the operating voltage is not maintained at a sufficient level, the data in the FRAM may fail to be written back into the FRAM cells, and may be irretrievably corrupted.
Normally, FRAMs are powered by a linear voltage regulator fabricated as a part of the FRAM die, with a large external filter capacitor. If, however, the external capacitor becomes shorted, or if shorts occur in other sections of the power management circuitry that create an immediate power loss on the FRAM supply voltage in the middle of read/write operation, the FRAM contents may be corrupted because the data write-back may not have been performed or completed.
What is needed, therefore, is a cost effective circuit and method to protect an FRAM during a power interruption, particularly during a read operation.